Chondroitin sulfate is a glycosaminoglycan. Would you expect to find this material within the lumen of the RER? Why or why not?

I origonally said no, because chondroitin sulfate gives off negative charges and Glycosaminoglycans (GAGs) are the building blocks of cartilage and joint fluid. However, I came to second guess myself, because I think glycosaminoglycans begin synthesis in the RER.